Developing A Wide Input Voltage DC-DC Converter

Digital power industry has evolved rapidly in the last decade for its superiorcharacteristics, which includes high adaptability, flexibility and reliability. Consideringthe complex power framework, long transmission distance and environmenttemperature down hole, power supply adopted there must not only be adjusted to thewide input voltage range, but also reach high power density and stability. Therefore,comprehensive factors should be took into account when designing power equipmentsutilized down hole to ensure safe and stable work.This paper is aiming at enhancing the adaptability of wide input voltage range,efficiency and stability of the new three level LLC converter, which is raised on thebasic of traditional half-bridge LLC topology. It fully takes advantage of excellentproperties of LLC topology, and meanwhile expanded its input voltage range andreduced its frequency range. Theoretical analysis and simulation has been studied forit and experimental results from prototype testing confirmed the theoretical analysis.Firstly, the driving scheme and operating modal are investigated respectively intwo or three level working mode. Duty cycle and switching sequence are determined foroptimal performance. Then we discussed the gain characteristic, soft switchingrequirements and unbalanced input capacitor voltage. After simulation with couplinginductance and parasitic parameters, the defects of fundamental wave analysis areimproved to obtain better circuit parameters. With key parameters obtained, we derivethe steady and small signal model of the main circuit to investigate on the frequencycharacteristics under varied input voltage and output loads. Compensation controllersare then designed according to the two or three level working mode and simulated inSimulink after building simulation modules of the multi-level LLC network and drivers.Simulation results verified the validity of the modeling and controller designing process.Based on the above theoretical analysis and simulation results, a100W wide inputthree level LLC digital power supply prototype is produced. The experimental resultsare in accordance with simulation results, which confirms the theoretical analysis.Whole input range automatic gain adjustments are realized within the setting frequencyrange and the controller could response fast when loads fluctuate or operating mode isswitched, which meets the design criterion.